A semiconductor module used for a power supply apparatus is widely applied for such consumer appliances as home air conditioners and refrigerators to such industrial equipment as inverters and servo controllers. To conserve power consumption in a semiconductor module, a power semiconductor element or the like is mounted on a circuit board, such as a metal base substrate or ceramic substrate. A semiconductor module is configured by mounting one or a plurality of circuit element(s) such as a power semiconductor element on a circuit board, adhering a plastic case frame and sealing with a silicone gel or epoxy resin.
On the other hand, a full mold semiconductor module made by a transfer molding method is used to reduce manufacturing cost (e.g. see Patent Document 1, identified further on). In a full mold semiconductor module, a lead frame and a heat sink are securely connected so as to ensure electric insulation.
FIG. 7 shows a first example of a conventional full mode semiconductor module. A power semiconductor element 7 and a drive IC 31 are mounted on lead frames 9B and 9C for external connection respectively, and are interconnected by bonding wires 11 and 12. These components are set in a metal mold and molding resin 14 is filled in, whereby the full mode semiconductor module is configured.
FIG. 8 shows a second example of a conventional full mode semiconductor module. In addition to the full mode semiconductor module illustrated in FIG. 7, a heat sink 32 is also disposed. The power semiconductor element 7 and the drive IC 31 are interconnected by the bonding wires 11 and 12, and the bonding wire 11 from the power semiconductor element 7 is bonded with a lead frame 9D for external connection.
FIG. 9 shows a third example of a conventional full mode semiconductor module. In the third example, an insulation substrate 33, which has the dual functions of an insulation layer and a heatsink, is included. For the insulation substrate 33, as illustrated in the figure, a metal base substrate constituted by a metal plate 34 and a copper foil 35, which are stacked via the insulation layer 36 made of resin, or a DBC (Direct Bond Copper) substrate of which insulation layer 36 is made of ceramic, for example, is used. The power semiconductor element 7 and the drive IC 31 are interconnected by bonding wires 11 and 12, and the power semiconductor element 7 is connected to a lead frame 9E for external connection via a bonding wire 11 and the copper foil 35.
FIG. 10 shows a fourth example of a conventional full mold semiconductor module. In the fourth example, an insulation metal block 37, where an insulation layer 2 is formed by spraying ceramic on one side of a metal block 1, is used instead of the insulation substrate 33 in FIG. 9. Since the power semiconductor element 7 is directly bonded with the metal block 1, some full mode semiconductor modules of this type have better coolability than the third example type. A bonding wire 11 from the power semiconductor element 7 is bonded with a lead frame 9F for external connection.
Patent Document 1: Japanese Patent Application Laid-open No. H9-139461 (paragraph number 0038, FIG. 1)
In the case of the conventional full mode semiconductor modules of the first to fourth examples, the bonding wire 11 is directly bonded to the power semiconductor element 7 and the other end of the bonding wire 11 is bonded to an external lead terminal, such as the lead frame 9B for external connection, and current is supplied from the external lead terminal, therefore heat generated when the power semiconductor element 7 is operating is conducted to the bonding wire 11 and the external lead terminal, which heats an external printed circuit board connected with the external lead terminal.
If the printed circuit board is heated, temperature inside a case of a power converter, such as an inverter, which houses the printed circuit board, increases, exceeding the heat resistance temperature of members in the power converter. This temperature increase could be handled by an air cooling or a water cooling method, but if either method were used the dimensions of the power converter would increase, which results in a cost increase. Therefore it is necessary to effectively control the temperature increase inside the case of the power converter without increasing the dimensions and cost of the power converter, and as one such countermeasure, it is demanded to effectively control heat that is conducted from the semiconductor module to the external printed circuit board via the external lead terminals.